Common English Prefixes and What They Mean: Decode Thousands of Words

A prefix is a small group of letters added to the front of a word to change its meaning. English has dozens of them, but a couple of dozen do most of the work. Learning them lets you make educated guesses about words you've never met.

Prefixes that mean "not" or "opposite"

• un-: unhappy, unlikely, unlock (also reverses an action)
• in- (with variants im-, il-, ir-): incorrect, impossible, illegal, irregular
• dis-: disagree, dislike, disappear
• non-: nonsense, nonfiction
• a- or an-: atypical, anonymous

The variants of in- change to fit the next letter: im- before m, p and b (immature, impatient), il- before l (illogical), and ir- before r (irresponsible).

Prefixes of time and order

• pre-: before (preview, prehistoric, prepay)
• post-: after (postpone, postgraduate)
• fore-: before or in front (forecast, foresee)
• ex-: former (ex-president) or out (exit, export)
• re-: again or back (rewrite, return, rebuild)

Prefixes of place and direction

• inter-: between (international, interact)
• trans-: across (transport, translate)
• sub-: under (submarine, subway)
• super-: above or beyond (supervise, superstar)
• over- and under-: too much or too little (overcook, undercharge)
• circum-: around (circumnavigate)
• ex- and extra-: outside or beyond (extraordinary)

Prefixes of number and size

• uni-: one (unicycle, uniform)
• bi-: two (bicycle, bilingual)
• tri-: three (triangle, tricycle)
• multi-: many (multinational)
• semi-: half (semicircle)
• micro- and macro-: small and large (microscope, macroeconomics)
• mega-: very large (megabyte)

Prefixes of attitude and relationship

• anti-: against (antisocial, antibiotic)
• pro-: for or forward (proactive, promote)
• co-: together (cooperate, coauthor)
• mis-: wrongly (misunderstand, misspell)
• mal-: badly (malfunction, malnutrition)
• auto-: self (automatic, autobiography)

Watch for false friends

Not every word beginning with these letters has the prefix. Interest doesn't mean "between rest", and uncle isn't the opposite of "cle". A word with a prefix should still make sense when you remove it: unhappy becomes happy, but uncle doesn't.

Hyphens

Prefixes are usually written without a hyphen (prehistoric), but many writers use one before a capital letter (anti-American), or to avoid awkward double letters (co-operate in some styles).

How to use this

1. When you meet a new word, look for a familiar prefix.
2. Remove it, and see whether what's left is a word you know.
3. Combine the meanings, and guess.
4. Check your guess in a dictionary.

A quick exercise

What might retroactive, hypersensitive and subtitle mean? Retro- means backward, hyper- means over or excessive, and sub- means under. A dictionary will confirm that you're close.

Check word meanings and origins with English Dictionary →